The present invention relates to ceramic articles, and more particularly to batch compositions and methods for producing ceramic articles comprised of a sintered phase aluminum titanate composition.
In diesel exhaust filtration, cordierite, being a low-cost material, in combination with offering low CTE, has been the material of choice. Porous cordierite ceramic filters of the wall-flow type have been utilized for the removal of particles in the exhaust stream from some diesel engines since the early 1980s. A diesel particulate filter (DPF) ideally combines low CTE (for thermal shock resistance), low pressure drop (for engine efficiency), high filtration efficiency (for removal of most particles from the exhaust stream), high strength (to survive handling, canning, and vibration in use), and low cost. Problems with cordierite include low volumetric heat capacity and low thermal conductivity which can result in unacceptably high temperatures during operation when the filters are regenerated under certain conditions, as well as low thermal durability. Further, inorganic particulates, known as ash, present in the diesel exhaust can react with cordierite and cause filter failures.
Aluminum titanate ceramic compositions have recently emerged as a viable alternative to the conventional cordierite ceramics due to their high volumetric heat capacity. Aluminum titanate is capable of forming ceramic articles of high, interconnected porosity and large median pore size, further combining high permeability, and being capable of employment in high temperature applications, such as diesel exhaust aftertreatment systems and diesel particulate filters. However, challenges surrounding the drying and firing of aluminum titanate precursor compositions make it difficult to obtain aluminum titanate ceramic filters with relatively high levels of porosity, tight dimensional tolerances, and crack-free filters following firing. While many approaches have been explored to increase the porosity of aluminum titanate, such as the addition of pore formers like potato starch and graphite, these approaches result in a decrease in the overall processing efficiency and corresponding increase in the material costs associated with the aluminum titanate production process.
Another challenge which exists in the production of aluminum titanate is the degree of deformation that occurs, like elephant's foot, during the firing process and that makes dimensional control an issue.
Still further, overall raw material costs associated with the inorganic aluminum titanate precursor compositions are significantly higher than those associated with conventional cordierite ceramics.
Therefore, for economical aluminum titanate production, there is a need in the art for ways of improving yields, reducing waste, and minimize the overall costs associated with the production of aluminum titanate ceramic compositions having the desired physical properties suitable for use in high temperature applications such as diesel particulate filtration systems.